For the exploration and production of oil, gas, and other hydrocarbons, a first step is to drill a relatively large diameter borehole. The drill string is then pulled out, and a steel pipe or casing is run into the wellbore. Typically, the casing is cemented in place in the surrounding formation. When the cement is sufficiently hardened, a new section is drilled, the drill string is tripped out, and a liner is hung off in the existing casing. Then the liner is cemented in place in the formation, and the process is repeated until the wellbore has reached the desired depth. It is also common to drill horizontal branches into geological layers containing hydrocarbons. A cased wellbore, therefore, is comprised of a series of pipe sections, the diameters of which decrease successively with the distance from the surface.
Cementing is usually accomplished by pumping cement slurry down the casing and out through a valve at the wellbore bottom so that it is discharged into the annulus between the formation and casing and flows back in an uphole direction. Once the annulus has been filled with fluid cement the cementing valve must be closed permanently before any excess cement is removed from the interior of the wellbore. In order to avoid that a lengthy pipe is filled with excess cement, it is common to insert separating plugs in front of and behind the cement flow. These separating plugs separate between a volume of cementing slurry and a circulation liquid (mud) in front of and behind the cement in the fluid flow. Therefore, a need exists for a valve that is able to be opened and closed several times in order to direct the various fluid flows to different locations before the valve is permanently closed.
Typically, a cemented section is perforated using a shaped explosive charge which pierces the casing and creates fractures in the surrounding formation so that hydrocarbons are able to flow into the well. Such explosive charges may potentially damage or destroy porous formations. Therefore, instead of using the above method involving cementing and explosive penetration, it may be desirable to provide a section with one or more valves and/or sand screens which can be opened when the well is put into production. It may also be desirable to be able to open and close such valves several times before they are opened or closed permanently.
At larger oil and gas fields it is common to drill injection wells at a distance from the production well(s). These are used for injecting fluids in order to increase the reservoir pressure and/or injecting chemicals in order to increase the production from the field. Also with injection wells there is a need for valves that can be opened and closed multiple times before they are permanently closed.
A sleeve valve is a type of valve commonly used in the above applications. The present invention is based on the same principle as other sleeve valves, in which an inner hollow shaft or sleeve is moved axially or rotated within an outer valve housing. When openings in the inner sleeve are aligned with openings in the outer housing the valve is open, and when the openings are not aligned, the valve is closed.
Numerous techniques are known for moving the inner sleeve relative to the outer valve housing, by way of a pipe string, a coiled tubing, or a well tractor, for example. In some applications, an actuation tool suspended from a cable (a “wireline”, or, if the cable carries power, “e-line”) may be used. As a last alternative is mentioned actuation through the use of a drop ball which is pumped or dropped down a pipe until it engages a seat of the tool to be actuated and blocks for further flow therethrough. Then, hydraulic pressure of the liquid column above the tool is used for activating or deactivating the valve. Any of these techniques or any other prior art method for opening or closing a sleeve valve in a wellbore may be used with the present invention.
In conventional technology, radially biased locking lugs are used for locking together an inner sleeve and an outer housing more or less permanently. A disadvantage of such locking lugs, in some applications, is that the spring providing the radial biasing force, whether it is a leaf spring, coil spring, or some other means, like the rest of the mechanism, must be made of a relatively expensive high quality steel material in order to avoid corrosion and wear. In other applications, it is important that the locking mechanism is shielded so that cement, drill cuttings, formation sand, etc, for example, are not able to get into the mechanism and prevent it from working properly. In other words, a need exists for a valve that can be closed permanently without the use of expensive steel qualities and/or sealing means.
The United States Patent Application US 2003/0192703 A1 describes various techniques for maintaining a valve flapper in an open position. Variants in which a collar run in on a tool and radially plastically deformed to lockingly engage an inner wall of the valve housing and thereby block for a flow pipe which, in turn, keeps the valve flapper in an open position, are described. A disadvantage of this method is that additional parts must be run down from the surface to retain the flapper in an open position.
Hence, a need exists for valves which can be opened and closed using conventional means, and which can be permanently kept in an open or closed end position.
Thus, the present invention provides a valve which is more robust, reliable, and inexpensive to fabricate than prior art valves for similar purposes, and which, moreover, is not encumbered with the above disadvantages.